Project Summary/Abstract Zika virus (ZIKV) infections remain an enduring public health challenge. An accurate test for the early and precise diagnosis of a ZIKV infection is urgently needed to control and to prevent the epidemic spreading of the disease. The proposal aims to identify new and comprehensive serological markers based on ZIKV specific IgM peptide epitopes at an early stage of the disease. The search for ZIKV specific biomarkers will be performed on proteome-wide high density peptide microarrays. To clearly discriminate Zika infections from related viral disorders such as Dengue virus (DENV), Yellow fever virus (YFV), West Nile virus (WNV) and Chikungunya virus (CHIKV) infections, the study will analyze IgM signatures in ZIKV patient sera in comparison to sera from patients with the aforementioned infections. High density peptide microarrays enable the analysis of antibody responses with unmet speed and precision, breaking down the immune response into immunogenic and specific peptide epitopes with single amino acid resolution. For the initial epitope discovery, a screening library will be used comprising the full proteomes of the most relevant subtypes of ZIKV, DENV, YFV, WNV and CHIKV. The proteome sequences will be translated into overlapping peptides and the resulting library will be synthesized on discovery microarrays with up to 35,000 different peptides per chip. The discovery arrays will be screened in a typical immunoassay with pooled sera of the different study groups. After the primary screening, the most specific biomarker candidates will be selected for further validation on focused second and third generation peptide microarrays with individual serum samples. After final validation, the most comprehensive peptide epitopes will be chosen as basis for a differential diagnostic device which allows the early and accurate ZIKV diagnosis that also enables the clear discrimination from DENV, YFV, WNV and CHIKV infections.